Safety fuse with glass coating on fusible portion

ABSTRACT

A safety fuse provided with a fusible element adapted for protection against overloads, the surface of said fusible element being covered with a continuous glass insulation coating. The fusible element may be a length of a cast microwire provided with a glass insulation.

United States Patent SAFETY FUSE WITH GLASS COATING ON FUSIBLE PORTION 4 Claims, 1 Drawing Fig.

US. Cl 337/ 159,

Int. Cl H0111 85/14 Field of Search 337/290, 185, 227, 159

[56] References Cited UNITED STATES. PATENTS 550,638 12/1895 McCulloch 2,532,078 12/1950 Baxter 2,833,890 5/1958 Jacobs, Jr... 3,341,674 9/1967 Jacobs, Jr 2,302,820 1 1/1942 Van Liempt... 3,009,040 1 1/1961 Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan Attorneywaters, Roditi, Schwartz & Nissen Bernstein 337/290( X) 337/290( X) 337/290(X) 337/290(X) 337/185 337/290 ABSTRACT: A safety fuse provided with a fusible element adapted for protection against overloads, the surface of said fusible element being covered with a continuous glass insulation coating. The fusible element may be a length of a cast microwire provided with a glass insulation.

fl 42A 1 PATENTED W25 Ian III SAFETY FUSE WITH GLASS COATING ON FUSIBLE PORTION The present invention relates generally to safety fuses adapted for protecting electric circuits against overloads, and more particularly to quick-operating safety fuses rated for low currents.

Known in the present state of the art are safety fuses provided with a fusible element which is enclosed in an envelope and surrounded by an insulating filling medium to prevent audible or luminous effect liable to occur in case of a blowout and for limiting short circuit current.

However, the above-mentioned safety fuses are insufficiently reliable in operation and feature short service lie, especially when used under the conditions of increased humidity of the ambient air; moreover, an increased blowing current observed in the aforementioned safety fuses makes them inapplicable for protection against overloads when low currents are involved.

Known heretofore are likewise safety fuses provided with fusible elements whose surfaces are silveror nickel-plated to protect said elements from being oxidized.

The above-mentioned safety fuses feature a limited overheating temperature of a fusible element as well as a limited pennissible temperature of environmental conditions under which the aforementioned safety fuse may be operable.

With all the above-said in view an object of the present invention is to eliminate the aforementioned disadvantages.

It is the main object of the present invention to provide a long service-life safety fuse to be applicable for operation under environmental conditions of increased humidity and temperature.

It is another object of the present invention to provide a simple-to-manufacture and inexpensive safety fuse.

It is still another object of the present invention to provide a reliable quick-operating safety fuse rated at low currents.

To accomplish the above-mentioned and other objects, the invention contemplates the provision in the safety fuse of a protection means adapted for preventing the fusible element from oxidizing and capable at the same time of providing operation under increased environmental temperature conditions, say of the order of 500 to 600 C.

Said object is accomplished by the fact that the safety fuse according to the present invention, features its fusible element whose entire surface is covered with a continuous glass insulating coating.

It is preferable that the fusible element, especially in case low currents are involved, be a length of a cast microwire provided with a glass insulation.

This makes it possible to provide for a mass production of reliable and long service-life safety fuses made of cast microwire provided with a glass insulation, the industrial production of said microwire being well known heretofore.

The invention will be described hereinbelow by way of exemplary embodiment thereof with due reference to the accompanying drawing the sole FIGURE of which represents an embodiment of a safety fuse provided with a fusible element, according to he invention.

Theoretical and experimental investigations conducted have shown that it is expedient, for increasing the environmental temperature conditions of fusible elements and the ampere-second characteristics of safety fuses rated at low currents, that a fusible element in the form of a length of wire be coated with a glass insulation. In this case the operating temperature conditions of the safety fuse in question will be determined by the melting temperature of the wire employed and the softening temperature of the glass which is applied to said wire. For example, when the wire is made ofcopper" and the glass insulation employed is of the types nonex" or pyrex," the temperature environmental conditions of the above-mentioned safety fuse may be maintained at a minimum current within the limits of 500 to 600 C.

The thickness of the glass insulation is within the limits of 2 to 15 mn and it does not substantially affect the melting cur- A length l of a cast microwire, provided with a glass insulation, is soldered in a gap 2 between the two portions 3 and 4 of a ceramic support 5, said portions being isolated from one another and coated with an electrically conducting foil.

The support 5 is supported on wire outlets 9 and 10 and is accommodated within a tubular case 6 which is closed at its ends with cups 7 and 8, through which extend wire outlets 9 and 10. i

We claim:

I. A safety fuse adapted for protection against overloads comprising a current conducting fusible element for insertion in an electrical circuit, a glass insulating coating covering the fusible element throughout the entire length thereof, an insulating support with first and second portions with a gap therebetween electrically conductive means on said first and second portions, said fusible element being electrically connected with said electrically conductive means on said portions and bridging said gap and lead wires connected to the respective electrically conductive means on said portions.

2. A safety fuse as claimed in claim 1 comprising a casing enclosing said support and fusible element, said lead wires passing through said casing.

3. A safety fuse as claimed in claim 2 wherein said casing is tubular and includes end cups through which said lead wires extend.

4. A safety fuse as claimed in claim 1, wherein said fusible element is a length of cast microwire. 

1. A safety fuse adapted for protection against overloads comprising a current conducting fusible element for insertion in an electrical circuit, a glass insulating coating covering the fusible element throughout the entire length thereof, an insulating support with first and second portions with a gap therebetween electrically conductive means on said first and second portions, said fusible element being electrically connected with said electrically conductive means on said portions and bridging said gap and lead wires connected to the respective electrically conductive means on said portions.
 2. A safety fuse as claimed in claim 1 comprising a casing enclosing said support and fusible element, said lead wires passing through said casing.
 3. A safety fuse as claimed in claim 2 wherein said casing is tubular and includes end cups through which said lead wires extend.
 4. A safety fuse as claimed in claim 1, wherein said fusible element is a length of cast microwire. 